Process of preparing fine-grain silverhalide emulsions

ABSTRACT

A method of preparing Lippmann-emulsions is described according to which the silver halide is precipitated in an aqueous hydrophilic colloid in the presence of the compound of the formula: Homogeneous emulsions are obtained with average silver halide grain-size smaller than 50 nm which show practically no scattering.

United States Patent 11 1 Philippaerts et al.

' [22] Filed:

l l PROCESS OF PREPARING FINE-GRAIN SILVERHALIDE EMULSIONS [73] Assignee: AGFA-Gevaert, Mortsel, Belgium Dec. 1, 1972 [2]] Appl. Nol: 311,161

[30], Foreign Application Priority Data Dec. 9 l97l Germany 2l6l044 [52] U.S'. Ci. 96/94 R, 96/1 l4.6 [51] Int. Cl G036 1/02 [58] Field Of Search. 96/94, 665, 114.6

[56] References Cited UNITED STATES PATENTS 3,661,592 5/1972 Philippaerts 96 94 1 51 Nov. 12, 1974 POllCI 96/94 Dersch )6/66.5

ll/l972 ll/l948 I Primary Examiner--Ronald H. Smith Assistant ExaminerJohn L. Goodrow Attorney, Agent, or Firm-A. W. Breiner [57] ABSTRACT A method of preparing Lippmann-emulsions is described according to which the silver halide is precipitated in an aqueous hydrophilic colloid in the presence of the compound of the formula:

, Homogeneous emulsions are obtained with average silver halide grain-size smaller than 50 nm which show.

practically no scattering.

5 Claims, No Drawings The present invention relates to the preparation of light-sensitive silver halide emulsions, more particularly to the preparation of fine-grain silver halide emulsions of the Lippmann type, to fine-grain silver halide emulsions prepared according to this method and to photographic elements having at least one layer of such a fine-grain silver halide emulsion.

Lippmann-emulsions, normally having an average grain-size of less than 100 nm, are of particular importance for the preparation of photographic plates or films with high resolution, for use in microphotography and in astrophotography, for recording nucleo-physical phenomenons, for the preparation of masks in the production of microelectronic integrated circuits, for use in holography, for high-density data storage, etc.

Nowadays there is an increasing demand for photographic plates or films having Lippmann-emulsion layers, the average grain-size of which is less than 50 nm. These materials are of particular importance for reflection-holograms where a high diffraction efficiency and a high signal to noise ratio are required.

Attempts to prepare Lippmann-emulsions with an average grain-size smaller than 50 nm by varying the working conditions during the precipitation of the silver halide, have not been successful.

In French Pat. No. l,553,483 it has been described to precipitate the silver halide inthe presence of heterocyclic mercapto compounds or tautomers thereof whereby very fine silver halide grains areobtained.

It has now been found that when effecting the precipitation of the silver halide in an aqueous hydrophilic colloid medium'in the presence of the compound having the following structural formula: W

silver halide emulsions are obtained the average grain size of which is even smaller than when effecting the precipitation in the presence of the corresponding heterocyclic mercapto compound l-phenyl-5-mercapto tetrazole.

The compound used according to the invention can be prepared as described in the published German patent application No. 1,597,503 by reaction of the sodium salt of l phenyl5-mercaptotetrazole with methyl chloroformate or with phosgene.

Though the above structural formula hasbeen given for the compound used according to the invention it is also possible that in the synthesis of this compound a product is formed which corresponds to an isomeric structure of said formula namely:

Since both isomers are useful for the purpose of the invention it should be understood that when one formula is given for the compound it is also intended to embrace the isomeric compound of the other formula.

By the use of the above compound duringthe precipitation step of the silver halide, homogeneous Lippmann-emulsions can be prepared with very small grain size so that emulsions are obtained practically without scattering.

The compound of use according to the present invention is generally added to the aqueous hydrophilic colloid composition, more particularly aqueous gelatin, into which the silver halide is precipitated. It can be used in amounts varying between very wide limits, preferably between 2 g and 20 g per mole of silver halide.

The ratio of hydrophilic colloid binder to silver halide in the fine-grain emulsions according to the present invention is preferably comprised between 0.2 and 6.0.

The hydrophilic colloid used as the vehicle for the silver halide may be any of the common hydrophilic colloids employed in photographic light-sensitive emulsions, for example gelatin, albumin, zein, casein, alginic acid, collodion, a cellulose derivative such as carboxymethyl cellulose, a synthetic hydrophilic colloid such as polyvinyl alcohol and poly-N-vinyl pyrrolidone, etcj mixtures of two or more colloids may be employed for dispersing the silver halide.

Various silver salts may be used as the light-sensitive salt such as silver bromide, silver chloride or mixed silv'er halides such as silver chlorobromide, silver bromo iodide and silver chlorobromoiodide. Emulsions containing silver bromide or silver chloride or a mixture of silver chloride and silver bromide and such emulsions containing small amounts of silver iodide up to 8 are favoured.

The silver halide emulsions of the Lippmann-type may be prepared according to methods well known in the art and described in the literature, see e.g. P. Glafkides Photographic Chemistry Vol. I, 1958, pages 365 to 368, Mees/James The theory of the Photographic Process 3rd edition (1966) p.36 and National Physical Laboratory Notes on Applied Science No. 20, Small Scale preparation of fine-grain (colloidal) Photographic Emulsions B. H. Crawford, London (1960). They may be prepared according to the technique described in our copending British patent application No. 15948/70.

After precipitation of the silver halide grains in the presence of the compounds of use according to the present invention the emulsion is washed in order to remove the water-soluble salts whereupon the emulsions may be chemically as well as spectrally sensitized.

They may be spectrally sensitized by any of the known spectral sensitizers such as cyanines and merocyanines for photographic silver halide materials. They may be chemically sensitized by means of sulphur compounds for example allyl thiocyanate, allyl thiourea, sodium thiosulphate, etc. They may also be sensitized by means of reductors for instance tin compounds, iminoamino methane sulphinic acids and derivatives thereof, cadmium salts, and small amounts of noble metal compounds such as gold, platinum, palladium, iridium, ruthenium and rhodium. The emulsions according to the invention may also comprise compoundswhich sensitize the emulsion by development acceleration for example compounds of the polyoxyalkylene type e.g. alkylene oxide condensation products 3 as described among others in U.S. Pat. Nos. 2,531,832 and 2,533,990, in U.K-. Pat. Specifications Nos. 920,637; 940,051;-945,340 and 991,608 and in Belgian Pat. No. 648,710 and the known onium compounds including quaternary ammonium, quaternary phosphonium and ternary sulphonium compounds.

Further, the emulsion may comprise antifoggants and stabilizers for example heterocyclic nitrogencontaining thioxo compounds such as benzothiazoline- 2-thione and 1-phenyl-2-tetrazoline-5-thione, compounds of the hydroxytriazolopyrimidine type such as 5-methyl-7-hydroxy-s-triazolo[1,5-a] pyrimidine and mercury compounds. They may also comprise lightabsorbing dyes to reduce scattering and reflection of light within the photographic material as described in Belgian Pat. No. 699,375 4 and British. Pat. No. 1,298,355.

Any of the hardening agents for hydrophilic colloids may be used in the emulsions according to the present invention for example formaldehyde, dialdehydes, diketones, halogen substituted aldehyde acids such as mucochloric acid and mucobromid acid, etc.

The emulsions may be coated on a wide variety of photographic emulsion supports. Typical supports include cellulose esterfilm, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film and related films of resinous materials as well as paper and glass. In

order to promote adhesion of the silver halide emulsions to glass supports it may be advantageous to use silicon compounds of the kind described in British Pat.

The following example illustrates the present invention.

EXAMPLE .erage grain size of 67 nm was obtained. Details as to the preparation of Lippmann-emulsions can be found amongst others in P. Glafkides, Photographic Chemistry" Vol. 1, 1958, Fountain Press, London.

Under completely analogous working conditions other emulsions were prepared with the difference that the aqueous solution of gelatin into which the sil- .ver bromide was precipitated now contained one of the compounds listed in the table below in an amount of 8.5 g per mole of silver nitrate used.

The average silver bromide grain size was determined 4 Theresults attained are listed in the table below.

Compound added 7 average grain- We claim:

1..Method of preparing a photographic fine-grain silver halide emulsion which comprises the step of precipitating the silver halide in an aqueous hydrophilic colloid medium in the presence of a compound having the formula; N N

2. Method according to claim 1, wherein said compound is present in the aqueous hydrophilic colloid me- 5. The photographic fine-grain silver halide emulsion of claim 4 wherein the emulsion is a silver bromide, silver chloride, or a silver chlorobromide emulsion.

=l l l= l 

1. A METHOD OF PREPARING A PHOTOGRAPHIC FINE-GRAIN SILVER HALIDE EMULSION WHICH COMPRISES THE STEP OF PRECIPITATING THE SILVER HALIDE IN AN AQUEOUS HYDROPHILLIC COLLOID MEDIUM IN THE PRESENCE OF A COMPOUND HAVING THE FORMULA:
 2. Method according to claim 1, wherein said compound is present in the aqueous hydrophilic colloid medium into which the silver halide is precipitated in an amount sufficient to effectively restrain growth of the silver halide grains.
 3. Method according to claim 1, wherein the emulsion is a silver bromide, silver chloride or a silver chlorobromide emulsion which may comprise a minor amount of silver iodide.
 4. A photographic fine-grain silver halide emulsion prepared by precipitating the silver halide in an aqueous hydrophilic colloid medium in the presence of a compound having the formula:
 5. The photographic fine-grain silver halide emulsion of claim 4 wherein the emulsion is a silver bromide, silver chloride, or a silver chlorobromide emulsion. 